An algorithm for encoding data for transmission in which each 64-bit data word is converted to a 66-bit transmission character.

Each transmission character is prefixed with either binary "01" or binary "10". This, combined with scrambling, gives the signal desirable engineering properties, yet incurs a much lower overhead than the traditional 8b/10b encoding.

A hardware devicetypically an add-in card or specialized component on a system boardthat converts the timing and protocol of one bus or interface to another, to enable a computer system's processing hardware to access peripheral devices.

One or more address identifiers that may be recognized by an N-Port in addition to its N-Port Identifier, used to form groups of N-Ports so that frames may be addressed to a group rather than to individual N-Ports.

1. The state of always having power applied (systems) or of being continually active (communication links).

2. A state of an operational link of always being powered on and continually transmitting either data frames, idles or fill words, in contrast to bursty transmissions and listening for a quiet line in earlier 10 and 100 Mbit/sec Ethernet.

A body that coordinates the development and use of voluntary consensus standards in the United States and represents the needs and views of U.S. stakeholders in international standardization forums around the globe.

ANSI accredits both standards certification organizations and standards development organizations. The IEEE Standards Association (which standardizes Ethernet and many other technologies) and INCITS (which standardizes SCSI, Fibre Channel, MPEG, and many other technologies) are two of over 100 ANSI accredited standards organizations.

At any instant, only one port in a Fibre Channel Arbitrated Loop can transmit data. Before transmitting data, a port in a Fibre Channel Arbitrated Loop must participate with all other ports in the loop in an arbitration to gain the right to transmit data. The arbitration logic is distributed among all of a loop's ports.

Any process by which a user of a shared resourcesuch as a port connected to a shared busnegotiates with other users for the (usually temporary) right to use the resource (in the given example, by transmitting data on the bus).

3.An organization of people and systems that have accepted the responsibility to protect, retain, and preserve information and data and make it available for a Designated Community. (Source: ISO 14721)

The amount of space on a system or data container which has been allotted to be written by an end user or application.

On thin provisioning systems, an assigned capacity number represents a promise that that amount of space will be provided on demand; usable capacity is allocated as the container is written. On fully provisioned systems, usable capacity must be committed at the same time the container is allocated. See thin provisioning.

A replication technique in which data must be committed to storage at only the primary site and not the secondary site before the write is acknowledged to the host. Data is then forwarded to the secondary site as the network capabilities permit.

A connection-oriented data communications technology based on switching 53 byte fixed-length units of data called cells.

ATM transmission rates are multiples of 51.840 Mbits per second. Each cell is dynamically routed. In the United States, a public communications service called SONET uses ATM at transmission rates of 155, 622, 2048, and 9196 Mbits per second. These are called OC-3, OC-12, OC-48, and OC-192 respectively. A similar service called SDH is offered in Europe. ATM is also used as a LAN infrastructure, sometimes with different transmission rates and coding methods than are offered with SONET and SDH.

An operation that, from an external perspective, occurs either in its entirety or not at all.

For example, database management systems that implement the concept of business transactions treat each business transaction as an atomic operation on the database. This means that either all of the database updates that comprise a transaction are performed or none of them are performed; it is never the case that some of them are performed and others not. RAID arrays must implement atomic write operations to properly reproduce single-disk semantics from the perspective of their clients.

Independent review and examination of records and activities to assess the adequacy of controls, to ensure compliance with established policies and operational procedures, and to recommend necessary changes in controls, policies, or procedures.

A chronological record of system activities that enables the reconstruction and examination of a sequence of events and/or changes in a system such as an information system, a communications system or any transfer of sensitive material and/or information.

A component of IPsec, standardized by the IETF, that permits the specification of various authentication mechanisms designed to provide connectionless integrity, data origin authentication, and an optional anti-replay service.

2. The property of being genuine and being able to be verified and trusted; confidence in the validity of a transmission, a message, or message originator. [NIST SP 800-53]

3. The property, condition, or quality of being worthy of trust, reliance, or belief because the proponent (offeror) has shown enough corroborating evidence to a jury (or trier of fact) to warrant such.

The substitution of a replacement unit (RU) in a system for a defective one, where the substitution is performed by the system itself while it continues to perform its normal function (possibly at a reduced rate of performance).

Automatic swaps are functional rather than physical substitutions, and do not require human intervention. Ultimately, however, defective components must be replaced in a physical hot, warm, or cold swap operation. See cold swap, hot swap, warm swap, hot spare.

1. The amount of time that a system is available during those time periods when it is expected to be available, often measured as a percentage of an elapsed year.

For example, 99.95% availability equates to 4.38 hours of downtime in a year (0.0005 * 365 * 24 = 4.38) for a system that is expected to be available all the time. See data availability, high availability.

2. The property of being accessible and usable upon demand by an authorized entity.

An IT installation's rules for how and when backup should be performed, such as which files or directories are to be backed up, the schedule on which backups should occur, which devices and media are eligible to receive the backups, how many copies are to be made, and actions to be performed if a backup does not succeed.

An interval of time during which a set of data can be backed up without seriously affecting applications that use the data.

For example, if an application accesses data from 8 AM until midnight, then the window between midnight and 8 AM is available for making backup copies. Offline backups require that applications not update data during the backup. Online backups typically use point in time copy technology to create consistent images of data for backup. If a backup uses different resources (storage devices, I/O paths, processing power) than the application, as is common with split mirror point-in-time copies, then the backup window is the time required to create the image. If the online backup shares resources with the applications using the data, as is common with copy-on-write point in time copies, the backup window may be increased due to resource contention.

The maximum rate of signal state changes per second on a communications circuit.

If each signal state change corresponds to a code bit, then the baud rate and the bit rate are the same. It is also possible for signal state changes to correspond to more than one code bit, so the baud rate may be lower than the code bit rate.

A classification of disk arraydata protection and mapping techniques developed by Garth Gibson, Randy Katz, and David Patterson in papers written while they were performing research into I/O subsystems at the University of California at Berkeley.

A relatively small program that resides in programmable, non-volatile memory on a personal computer and that is responsible for booting that computer and performing certain operating system independent I/O operations.

Standard BIOS interrupts are defined to allow access to the computer's disk, video and other hardware components (for example, INT13 for disk access).

The BER is measured by counting the number of bits in error at the output of a receiver and dividing by the total number of bits in the transmission. BER is typically expressed as a negative power of 10.

A computer or storage system composed of a chassis that provides power, cooling and other common infrastructure, and one or more removable server or storage units, usually called blades.

Blade systems are designed as a scalable solution to efficiently package and operate multiple processing or storage units in a single enclosure, and are designed for technicians to be able to easily add or replace hot-swappable boards in the field.

The act of applying virtualization to one or more block based (storage) services for the purpose of providing a new aggregated, higher levele.g., richer, simpler, more secureblock service to clients.

The process of loading Operating System code from a disk or other storage device into a computer's memory and preparing it to run.

Bootstrapping is an appropriate term since a code load typically occurs in steps, starting with a very simple program (BIOS) that initializes the computer's hardware and reads a sequence of data blocks from a fixed location on a pre-determined disk, into a fixed memory location. The data thus read is the code for the next stage of bootstrappingusually an operating system loader. The loader completes the hardware setup and results in an executing operating system, in memory.

1. A Fibre Channel technology that provides a transparent fabric extension between two switch E-Ports through the use of 2 B-Ports tunneling through some alternative technology, resulting in an Inter-Switch Link (ISL) that "appears" to be a direct link between switches.

For example, a bridge pair can take an incoming Fibre Channel frame from one B-Port on a Bridge, encapsulate that frame using FCIP (Fibre Channel over IP) and transmit the frame as payload over an IP network to the remote Bridge where the original frame is forwarded to the remote Fibre Channel Fabric switch E-Port through the remote Bridge's B-Port.

2. A Fibre Channel technology that enables traffic carried along part of the path from a source device by Fibre Channel, (for example commands, blocks, status and control between a SCSIinitiator or target source device) to be extended to the destination device using an alternative physical transport network technology (for example iSCSI or SCSI Interconnect).

In some cases this "Bridge" is also referred to as a physical transport gateway, or storage router.

3. A device that connects multiple LAN segments at the physical address layer.

As opposed to a hub, which indiscriminately rebroadcasts everything from one segment to the other, a bridge only retransmits traffic from one segment to another when the traffic is intended for the destination segment.

The simultaneous transmission of a message to all receivers (ports) connected to a communication facility.

Broadcast can be contrasted with unicast (sending a message to a specific receiver) and multicast (sending a message to select subset of receivers). In a Fibre Channel context, broadcast specifically refers to the sending of a message to all N-Ports connected to a fabric. See multicast, unicast.

A port indicates the number of frames that can be sent to it (its buffer credit) before the sender is required to stop transmitting and wait for the receipt of a "ready" indication. Buffer to buffer flow control is used only when an NL-Port is logged into another NL-Port on an Arbitrated Loop or when an Nx-Port is logged into an FX-Port." or "Flow control that occurs between two directly connected Fibre Channel ports, e.g., an N_Port and its associated F_Port or between two E_Ports. A port indicates the number of frames that can be sent to it (its buffer credit), before the sender is required to stop transmitting and wait for the receipt of additional credit.

Canisters are usually designed to mount in shelves that supply power, cooling, and I/O interconnect services to the devices. They are used to minimize RF emissions and to simplify insertion and removal of devices in multi-device storage subsystems. See shelf.

A physical layer data transmission protocol used in Ethernet and fast Ethernet networks.

Carrier sense refers to arbitration for a shared link. Unlike "always on" physical protocols, carrier sense protocols require a node wishing to transmit to wait for the absence of carrier (indicating that another node is transmitting) on the link. Multiple access refers to the party line nature of the link. A large number of nodes (up to 500 in the case of Ethernet) share access to a single link. Collision detection refers to the possibility that two nodes will simultaneously sense absence of carrier and begin to transmit, interfering with each other. Nodes are required to detect this interference, and cease transmitting. In the case of Ethernet, each node detecting a collision is required to wait for a random interval before attempting to transmit again.

A process that tracks the movement of evidence through its collection, safeguarding, and analysis lifecycle by documenting each person who handled the evidence, the date/time it was collected or transferred, and the purpose for the transfer. [NIST SP 800-72]

The term channel has other meanings in other branches of computer technology. The definitions given here are commonly used when discussing storage and networking. See device channel, I/O interconnect, host I/O bus.

1. The recorded state of an application at an instant of time, including data, in-memory variables, program counter, and all other context that would be required to resume application execution from the recorded state.

2. An activity of a file system, such as the High Performance File System, (HPFS) or the Andrew File System (AFS), in which cached metadata (data about the structures of the file system) is periodically written to the file system's permanent store, allowing the file system to maintain consistency if an unexpected stop occurs.

A connection-oriented class of Fibre Channel communication service in which the entire bandwidth of the link between two ports is dedicated for communication between the ports and not used for other purposes.

Fibre Channel classes of service include connection-based services (Class 1), acknowledged frame delivery with end to end flow control (Class 2), and packetized frame datagrams (Class 3). Different classes of service may simultaneously exist in a fabric. The form and reliability of delivery in Class 3 circuits may vary with the topology.

A form of human interface to intelligent devices characterized by non-directive prompting and character string user input.

CLIs are used by system consoles and remote shell sessions (RSH, SSH). They are very useful for scripting and other administrative purposes, but are usually perceived by end users to be more difficult to comprehend and use than graphical user interfaces (GUIs).

CIM is divided into a Core Model and Common Models. The Core Model addresses high-level concepts (such as systems and devices), as well as fundamental relationships (such as dependencies). The Common Models describe specific problem domains such as computer system, network, user or device management. The Common Models are subclasses of the Core Model and may also be subclasses of each other.

CIFS was originally called Server Message Block (SMB). Today, other implementations of the CIFS protocol allow other clients and servers to use it for intercommunication and interoperation with Microsoft operating systems.

The most common complex arrays are multi-level disk arrays, which perform more than one level of data address mapping, and adaptive arrays, which are capable of changing data address mapping dynamically.

These architectures enable improvements in application performance and/or infrastructure efficiency through the integration of compute resources (outside of the traditional compute & memory architecture) either directly with storage or between the host and the storage. The goal of these architectures is to enable parallel computation and/or to alleviate constraints on existing compute, memory, storage, and I/O.

A logical joining of two series of data, usually represented by the symbol "|".

In data communications, two or more datums are often concatenated to provide a unique name or reference (e.g., S-ID | X-ID). Volume managers concatenate disk address spaces to present a single larger address spaces.

A hybrid point in time copy mechanism which creates a split mirror copy by copying blocks from the source as they are requested by the host, while copying so-far unrequested blocks in the background until the mirror is complete.

A concurrent copy initially occupies at least the amount of storage required to hold accessed blocks and grows to occupy as much storage as the copy source.

1. The process of installing or removing hardware or software components required for a system or subsystem to function.

2. Assignment of the operating parameters of a system, subsystem or device, such as designating a disk array's member disks or extents and parameters such as stripe depth, RAID model, cache allowance, etc.

The management of system features and behaviors through the control of changes made to hardware, software, firmware documentation and related resources throughout the life cycle of an information system.

1. A device for graphical or textual visual output from a computer system.

2. In systems, network and device management, an application that provides graphical and textual feedback regarding operation and status, and that may accept operator commands and input influencing operation and status.

Sophisticated consoles designed for the management of many systems from one location are sometimes called enterprise management consoles.

A body of software that provides common control and management for one or more disk arrays or tape arrays.

Control software presents the arrays of disks or tapes it controls to its operating environment as one or more virtual disks or tapes. Control software may execute in a disk controller or intelligent host bus adapter, or in a host computer. When it executes in a disk controller or adapter, control software is often referred to as firmware.

1. The control logic in a disk or tape that performs command decoding and execution, host data transfer, serialization and deserialization of data, error detection and correction, and overall management of device operations.

A technique for maintaining a point in time copy of a collection of data by copying only data that is modified after the instant of replicate initiation; the original source data is used to satisfy read requests for both the source data itself and for the unmodified portion of the point in time copy.

The replacement of a properly functioning arraymember by another disk, including copying of the member's contents to the replacing disk.

Copyback, which is most often used to create or restore a particular physical configuration for an array (e.g., a particular arrangement of array members on device I/O interconnects), is accomplished without reduction of the array.

A disk data organization model in which the disk is assumed to consist of a fixed number of tracks, each having a maximum data capacity.

Multiple records of varying length may be written on each track of a Count-Key-Data disk, and the usable capacity of each track depends on the number of records written to it. The CKD architecture derives its name from the record format, which consists of a field containing the number of bytes in the key and data fields and a record address, an optional key field by which particular records can be easily recognized, and the data itself. CKD is the storage architecture used by IBM Corporation's System 390 series of mainframe computer systems. See fixed block architecture.

A method for rendering encrypted data unrecoverable by securely deleting the keying material required to decrypt the data.

The encrypted data itself is not modified. The protection offered by cryptographic erasure is bounded by the work factor involved in discovering the decryption key or mounting a cryptanalytic attack on the encryption algorithm itself.

A function that maps plaintext strings of any length to bit strings of fixed length, such that it is computationally infeasible to find correlations between inputs and outputs, and such that given one part of the output, but not the input, it is computationally infeasible to predict any bit of the remaining output.

A scheme for checking the integrity of data that has been transmitted or stored and retrieved.

A CRC consists of a fixed number of bits computed as a function of the data to be protected, and appended to the data. When the data is read or received, the function is recomputed, and the result is compared to that appended to the data. Cyclic redundancy checks differ from error correcting codes in that they can detect a wide range of errors, but are not capable of correcting them. See error correcting code.

Lossy compression (i.e., compression using a technique in which a portion of the original information is lost) is acceptable for some forms of data (e.g., digital images) in some applications, but for most IT applications, lossless compression (i.e., compression using a technique that preserves the entire content of the original data, and from which the original data can be reconstructed exactly) is required.

The policies, processes, practices, services and tools used to align the business value of data with the most appropriate and cost-effective storage infrastructure from the time data is created through its final disposition.

Data is aligned with business requirements through management policies and service levels associated with performance, availability, recoverability, cost, etc. DLM is a subset of ILM.

A set of services that control of data from the time it is created until it no longer exists.

Data Management Services are not in the data path; rather, they provide control of, or utilize, data in the delivery of their services. This includes services such as data movement, data redundancy, and data deletion.

The length of the statistically expected continuous span of time over which data stored by a population of identical storage subsystems can be correctly retrieved, expressed as Mean Time to Data Loss (MTDL).

Preserving the existence and integrity of data for some period of time or until certain events have transpired, or any combination of the two.

Retention requirements are expressed either as a time period, an event (e.g., the death of a patient), or a combination (e.g., 3 years after said death). Multiple requirements may be active, and some (e.g., judicial holds) may trump others.

A process for deleting data that is intended to make the data unrecoverable.

One such process consists of repeated overwrites of data on disk. Data shredding is not generally held to make data completely unrecoverable in the face of modern forensic techniquesthat requires shredding of the disks themselves. Forensic techniques, however, do require physical access to the storage media.

Disk striping is commonly called RAID Level 0 or RAID 0 because of its similarity to common RAID data mapping techniques. It includes no redundancy, however, so strictly speaking, the appellation RAID is a misnomer.

The data transfer capacity of an I/O subsystem is an upper bound on its data transfer rate for any I/O load. For disk subsystem I/O, data transfer rate is usually expressed in MBytes/second (millions of bytes per second, where 1 million = 106) or Gbits/second (billions of bits per second, where 1 billion = 109). See data transfer capacity.

An set of computer programs with a user and/or programming interface that supports the definition of the format of a database and the creation of and access to its data.

A database management system removes the need for a user or program to manage low level database storage. It also provides security for and assures the integrity of the data it contains. Types of database management systems are relational (table-oriented), network, hierarchical and object oriented.

1. A procedure that renders data unreadable by applying a strong magnetic field to the media.

2. Applying a degaussing procedure.

Degaussing is also called demagnetizing and erasure. Both of these terms are misleading, because in magnetic digital media the individual magnetic domains are not erased or demagnetized, but simply made to line up in the same direction, which eliminates any previous digital structure.

A protocol defined by the IETF for managing network traffic based on the type of packet or message being transmitted.

The Differentiated Services protocol is often abbreviated as DiffServ. DiffServ rules define how a packet flows through a network based on a 6 bit field (the Differentiated Services Code Point) in the IP header. The Differentiated Services Code Point specifies the "per hop behavior" (bandwidth, queuing and forward/drop status) for the packet or message.

Digital object auditing is a process of routine periodic testing of stored digital objects, usually using cryptographic techniques, by comparing their previous signatures and time stamps to their current to verify that change, loss of access, or data loss has not occurred.

A preservation object provides the functionality required to assure the future ability to use, secure, interpret, and verify authenticity of the metadata, information, and data in the container and is the foundational element for digital preservation of information and data.

A digital preservation service includes a comprehensive management and curation function that controls its supporting infrastructure, information, data, and storage services in accordance with the requirements of the information objects it manages to accomplish the goals of digital preservation.

Digital signatures can generally be externally verified by entities not in possession of the key used to sign the information. For example, a secure hash of the information encrypted with the originator's private key when an asymmetric cryptosystem is used. Some algorithms that are used in digital signatures cannot be used to encrypt data. (e.g., DSA).

The secret key used in DSA operates on the message hash generated by SHA-1; to verify a signature, one recomputes the hash of the message, uses the public key to decrypt the signature and then compares the results.

Directories are usually organized hierarchically. I.e., a directory may contain both information about files and objects, and other directories. They are used to organize collections of files and other objects for application or human convenience.

2. A file or other persistent data structure in a file system that contains information about other files.

3. An LDAP-based repository consisting of class definitions and instances of those classes.

DEN's goals are to provide a consistent and standard data model to describe a network, its elements and its policies/rules. Policies are defined to provide quality of service or to manage to a specified class of service.

The recovery of data, access to data and associated processing through a comprehensive process of setting up a redundant site (equipment and work space) with recovery of operational data to continue business operations after a loss of use of all or part of a data center.

This involves not only an essential set of data but also an essential set of all the hardware and software to continue processing of that data and business. Any disaster recovery may involve some amount of down time.

1. Process by which each party obtains information held by another party or non-party concerning a matter. [ISO/IEC 27050-1]

Discovery is applicable more broadly than to parties in adversarial disputes. Discovery is also the disclosure of hardcopy documents, Electronically Stored Information and tangible objects by an adverse party. In some jurisdictions the term disclosure is used interchangeably with discovery.

2. The process of finding devices attached to a storage infrastructure.

3. The process of finding network interfaces in a networking infrastructure.

A set of disks from one or more commonly accessible disk subsystems, combined with a body of control software.

The control software presents the disks' storage capacity to hosts as one or more virtual disks. Control software is often called firmware or microcode when it runs in a disk controller. Control software that runs in a host computer is usually called a volume manager.

Disk blocks are of fixed usable size (with the most common being 512 bytes), and are usually numbered consecutively. Disk blocks are also the unit of on-disk protection against errors; whatever mechanism a disk employs to protect against data errors (e.g., ECC) protects individual blocks of data. Seesector.

This definition includes rotating magnetic and optical disks and solid-state disks, or non-volatile electronic storage elements. It does not include specialized devices such as write-once-read-many (WORM) optical disks, nor does it include so-called RAM disks implemented using software to control a dedicated portion of a host computer's volatile random access memory.

1. A Windows server that contains a copy of a user account database. A Windows domain may contain both primary and backup domain controllers.

2. The control function accessible directly by an N-Port attached to a switch and also addressable in other domains using the Domain Controller address identifier of ""FF FC nn"" hex, where nn is the remote Domain Controller being accessed.

A computer program that converts between IP addresses and symbolic names for nodes on a network in a standard way.

Most operating systems include a version of DNS. The service is defined by the IETF Standard RFCs 974, 1034, 1035, 1122, and 1123, and over a hundred subsequent RFCs that have not yet achieved full standard status.

A technique used to increase data transfer rate by constantly keeping two I/O requests for consecutively addressed data outstanding.

A software component begins a double-buffered I/O stream by making two I/O requests in rapid sequence. Thereafter, each time an I/O request completes, another is immediately made, leaving two outstanding. If a disk subsystem can process requests fast enough, double buffering allows data to be transferred at a disk or disk array's full volume transfer rate.

A pair of components, such as the controllers in a failure tolerant storage subsystem that share a task or class of tasks when both are functioning normally, but take on the entire task or tasks when one of the components fails.

Dual active controllers are connected to the same set of storage devices, and improve both I/O performance and failure tolerance compared to a single controller. Dual active components are also called active-active components.

The responsibility that managers and their organizations have a duty to provide for information security to ensure that the type of control, the cost of control, and the deployment of control are appropriate for the system being managed. [NIST SP 800-30]

The amount of data stored on a storage system, plus the amount of unused formatted capacity in that system.

There is no way to precisely predict the effective capacity of an unloaded system. This measure is normally used on systems employing space optimization technologies.

An estimated calculation may be made as follows. Let D = the size of data already stored, Fd be the formatted capacity used to store that data, and Ft be the total formatted capacity on the system. Then the estimated effective capacity Ee is given by the formula Ee = D / (Fd / Ft). No unused formatted capacity is used in the estimation calculation.

The efficiency of any electrical device which transforms one type of power into another.

Efficiency is defined as output power divided by input power expressed as a percentage. All electrical components in a computer system, such as PDUs, UPSs and power supplies, incur some degree of power loss. Determining the total power loss in smaller systems with one power supply can be done by straightforward measurement of wall plug power and the total power supplied at the power supply's outputs. Larger systems require more complex methods.

Data or information of any kind and from any source, whose temporal existence is evidenced by being stored in, or on, any electronic medium. [ISO/IEC 27040]

Electronically Stored Information (ESI) includes traditional e-mail, memos, letters, spreadsheets, databases, office documents, presentations, and other electronic formats commonly found on a computer. ESI also includes system, application, and file-associated metadata (3.26) such as timestamps, revision history, file type, etc. Electronic medium can take the form of, but is not limited to, storage devices and storage elements.

Defines a uniform taxonomy of storage subsystems and a standard way of measuring power efficiency of the storage subsystems defined in the taxonomy. For more detailed information, please consult the SNIA Emerald Program website (https://www.snia.org/emerald).

While power and energy efficiency look about the same to a layman, the numbers may be different (even neglecting the units) on account of temporal variations in supply voltages, power and load factors and so on.

Software that manages all aspects of an organization's assets, systems, services and functions.

ERM systems manage a set of resources in the wider perspective of an organization's entire business. Managing in an enterprise context requires that entities be named uniquely and locatable within the enterprise, that heterogeneity of platforms and services may be assumed, and that the dynamic nature of the environment is taken into account.

A measure of the amount of uncertainty that an attacker faces to determine the value of a secret. [NIST SP 800-63]

The value is sometimes measured in bits of security strength, where a value of 0 indicates no security strength (i.e., full predictability or no randomness) and a positive value indicates increasing security strength.

A forward error correction technology used to provide data resiliency and long-term data integrity, by spreading data blocks and parity information across multiple storage devices or systems that may be in multiple physical locations.

Both the level of resiliency and where erasure coding is applied (at the array, at the node, or at the system level) can significantly affect how much processing overhead it consumes.

A scheme for checking the correctness of data that has been stored and retrieved, and correcting it if necessary.

An ECC consists of a number of bits computed as a function of the data to be protected, and appended to the data. When the data and ECC are read, the function is recomputed, the result is compared to the ECC appended to the data, and correction is performed if necessary. Error correcting codes differ from cyclic redundancy checks in that the latter can detect errors, but are not generally capable of correcting them. See cyclic redundancy check.

The SNIA uses the base 10 convention commonly found in I/O-related and scientific literature rather than the base 2 convention (1,152,921,504,606,846,976, i.e., 260) common in computer system and software literature.

The SNIA uses the base 10 convention commonly found in I/O-related and scientific literature rather than the base 2 convention (1,152,921,504,606,846,976, i.e., 260) common in computer system and software literature.

A set of one or more non-concurrent related sequences passing between a pair of Fibre Channel ports.

An exchange encapsulates a "conversation" such as a SCSI task or an IP exchange. Exchanges may be bidirectional and may be short or long lived. The parties to an exchange are identified by an Originator Exchange-Identifier (OX-ID) and a Responder Exchange_Identifier (RX_ID).

A single disk may be organized into multiple extents of different sizes, and may have multiple (possibly) non-adjacent extents that are part of the same virtual disk-to-member disk array mapping. This type of extent is sometimes called a logical disk.

A diagram used to specify optical or electrical signal transition characteristics for transmitters, in which the horizontal axis represents normalized time from pulse start and the vertical axis represents normalized amplitude.

The restoration of a failed system component's share of a load to a replacement component after a failback event.

When a failed controller in a redundantconfiguration is replaced, the devices that were originally controlled by the failed controller are usually failed back to the replacement controller to restore the I/O balance, and to restore failure tolerance. Similarly, when a defective fan or power supply is replaced, its load, previously borne by a redundant component can be failed back to the replacement part.

A mode of operation for failure tolerant systems in which a component has failed and its function has been assumed by a redundant component.

A system that protects against single failures operating in failed over mode is not failure tolerant, since failure of the redundant component may render the system unable to function. Some systems (e.g., clusters) are able to tolerate more than one failure; these remain failure tolerant until no redundant component is available to protect against further failures.

The automatic substitution of a functionally equivalent system component for a failed one.

The term failover is most often applied to intelligent controllers connected to the same storage devices and host computers. If one of the controllers fails, failover occurs, and the survivor takes over its I/O load.

The ability of a system to continue to perform its function (possibly at a reduced performance level) when one or more of its components has failed.

Failure tolerance in disk subsystems is often achieved by including redundant instances of components whose failure would make the system inoperable, coupled with facilities that allow the redundant components to assume the function of failed ones.

A technique for reducing the time required to synchronize a split mirror with the set of storage devices from which it was split.

Fast mirror resynchronization requires that a list of changes to the original set of data since moment of splitting be kept. When the split mirror is rejoined to the original set of volumes, only the data items identified in the list are copied from the original to the split mirror rather than the entire contents of the devices.

In this and other FC-related entries, the numbers denote versions of the spec, developed and maintained by the INCITS T11 committee, that bears that name. The listed version is current as of this writing.

A Fibre Channel Switching Device with one or more Lossless Ethernet MACs, each coupled with an FCoE Controller, and optionally one or more Lossless Ethernet bridging devices and optionally an FC Fabric interface.

An FCF forwards FCoE frames addressed to one of its FCF-MACs based on the D_ID of the encapsulated FC frames.

Both FDDI-fiber adapters that connect to optical fiber FDDI networks, and FDDI-TP adapters that connect to twisted copper pair FDDI networks exist. Although network interface cards are usually referred to as NICs rather than as adapters, the term FDDI adapter is more common than FDDI NIC. See NIC.

FibreChannel supports point to point, arbitrated loop, and switched topologies with a variety of copper and optical links running at speeds from 1 Gb/s to 10 Gb/s. The committee standardizing Fibre Channel is the INCITS Fibre Channel (T11) Technical Committee.

Nodes connected to a Fibre Channel Arbitrated Loop arbitrate for the single transmission that can occur on the loop at any instant using a Fibre Channel Arbitrated Loop protocol that is different from Fibre Channel switched and point to point protocols. An arbitrated loop may be private (no fabric connection) or public (attached to a fabric by an FL_Port). The network is defined by the FC-AL-2 standard INCITS 332 - 1999 [R2004].

A mutual benefit corporation formed under the non-profit corporation laws of the State of California, whose members consist of companies that manufacture Fibre Channel systems, components, software, and tools, as well as provide Fibre Channel education and services to end-user customers.

A technical report specifying common methodologies for both arbitrated loop and switched environments, with the intention of facilitating interoperability between devices whether they are connected in a loop or Fabric topology.

An ANSI standard that describes the protocols used to implement security in a Fibre Channel fabric.

This standard includes the definition of protocols to authenticate Fibre Channel entities, protocols to set up session keys, protocols to negotiate the parameters required to ensure frame-by-frame integrity and confidentiality, and protocols to establish and distribute policies across a Fibre Channel fabric.

An abstract data object made up of (a.) an ordered sequence of data bytes stored on a disk or tape, (b.) a symbolic name by which the object can be uniquely identified, and (c.) a set of properties, such as ownership and access permissions that allow the object to be managed by a file system or backup manager.

Unlike the permanent address spaces of storage media, files may be created and deleted, and in most file systems, may expand or contract in size during their lifetimes.

A namespace-based network-oriented infrastructure for files that includes a decoupling layer that separates logical file access from physical file location, and enables a variety of services (e.g., replication and migration) to be applied to files and file systems.

A software component that imposes structure on the address space of one or more physical or virtual disks so that applications may deal more conveniently with abstract named data objects of variable size (files).

File systems are often supplied as operating system components, but are also implemented and marketed as independent software components.

Spelling filesystem as a single word is also correct, especially when the term is used as an adjective.

An FL-Port becomes a shared entry point for public NL-Port devices to a Fibre Channel fabric. FL-Ports are intermediate ports in virtual point-to-point links between end ports that do not reside on the same loop, for example the NL-Port on an end node to the FL-Port on a switch to the F-Port in that switch to the N_Port on that end node through a single Fibre Channel fabric switch.

An accurate bit-for-bit reproduction of the information contained on an electronic device or associated media, whose validity and integrity has been verified using an accepted algorithm. [NIST SP 800-72]

The preparation of a disk for use by writing required information on the media.

Disk controllers format disks by writing block header and trailer information for every block on the disk. Host software components such as volume managers and file systems format disks by writing the initial structural information required for the volume or file system to be populated with data and managed.

In a simple world, free space is normally the same as assigned capacity less the amount of assigned capacity already written. But restrictions such as quotas and interactions between systems using different arithmetic may cause the reported free space to vary from the actual quantity.

The average rate at which a single disk transfers a large amount of data (e.g., more than one cylinder) in response to one I/O request.

The full-volume data transfer rate accounts for any delays (e.g., due to inter-sector gaps, inter-track switching time and seeks between adjacent cylinders) that may occur during the course of a large data transfer. Full volume transfer rate may differ depending on whether data is being read or written. If this is true, it is appropriate to speak of full-volume read rate or full-volume write rate. Also known as spiral data transfer rate.

F_Ports are intermediate ports in virtual point-to-point links between end system ports, for example the N_Port on an end node to the F_Port on a switch to the F_Port in that switch to the N_Port on the other end node using a single Fibre Channel fabric switch. An F_Port is assumed to always refer to a port to which non-loop PN_Ports are attached to a Fabric, and does not include FL_Ports [FC-FS-2].

Garbage collection has uses in many aspects of computing and storage. For example, in flash storage, background garbage collection can improve write performance by reducing the need to perform whole block erasures prior to a write. See also trim.

The primary aspects of a disk's geometry are the number of recording bands and the number of tracks and blocks per track in each, the number of data tracks per cylinder, and the number and layout of spare blocks reserved to compensate for media defects.

The SNIA uses the base 10 convention commonly found in I/O-related and scientific literature rather than the base 2 convention (1,073,741,824, i.e., 230) common in computer system and software literature.

For Fibre Channel, this refers to a bit transmission rate of 1,062,500,000 bits per second.

The SNIA uses the base 10 convention commonly found in I/O-related and scientific literature rather than the base 2 convention (1,073,741,824, i.e., 230) common in computer system and software literature.

A GL-Port can determine operating mode at switch port initialization, FL-Port when an NL-Port attachment is determined, F-Port when an N_Port attachment is determined, E_Port when an E_Port attachment is determined.

A zone consisting of zone members that are permitted to communicate with one another via the fabric.

Hard zones are enforced by fabric switches that prohibit communication among members not in the same zone on a frame by frame basis, based on the source and destination addressing. Well-known addresses are implicitly included in every zone.

A value calculated over the contents of a message (usually using a cryptographic hash algorithm) that can be used to demonstrate that the contents of the message have not been changed during transmission.

The automated migration of data objects among storage devices, usually based on inactivity.

Hierarchical storage management is based on the concept of a cost-performance storage hierarchy. By accepting lower access performance (higher access times), one can store objects less expensively. By automatically moving less frequently accessed objects to lower levels in the hierarchy, higher cost storage is freed for more active objects, and a better overall cost to performance ratio is achieved.

The ability of a system to perform its function continuously (without interruption) for a significantly longer period of time than the reliabilities of its individual components would suggest.

High availability is most often achieved through failure tolerance. High availability is not an easily quantifiable term. Both the bounds of a system that is called highly available and the degree to which its availability is extraordinary must be clearly understood on a case-by-case basis.

Host cache may be associated with a file system or database, in which case, the data items stored in the cache are file or database entities. Alternatively, host cache may be associated with the device driver stack, in which case the cached data items are sequences of disk blocks. See cache, controller cache, disk cache.

The term host environment is used in preference to host computer to emphasize that multiple host computers are being discussed, or to emphasize the importance of the operating system or other software in the discussion.

A redundant component in a failure tolerant subsystem that is powered and ready to operate, but that does not operate as long as all of its target primary components are functioning.

Hot standby components increase storage subsystemavailability by allowing systems to continue to function when a component such as a controller fails. When the term hot standby is used to denote a disk, it specifically means a disk that is spinning and ready to be written to, for example, as the target of a rebuilding operation.

A communications infrastructure element to which nodes on a multi-point bus or loop are physically connected.

Commonly used in Ethernet and Fibre Channel networks to improve the manageability of connecting devices to a bus structure, both managing physical cables and supporting the addition or removal of nodes from the bus while it is operating. Hubs maintain the logical loop topology of the network of which they are a part, while creating a "hub and spoke" physical star layout. Unlike switches, hubs do not aggregate bandwidth.

A composition of two or more clouds (private, community, or public) that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability.

I/O is the process of moving data between a computer system's main memory and an external device or interface such as a storage device, display, printer, or network connected to other computer systems. This encompasses reading, or moving data into a computer system's memory, and writing, or moving data from a computer system's memory to another location.

In the context of storage subsystems, I/O adapters are contrasted with embedded storage controllers, that not only adapt between buses and interconnects, but also perform transformations such as device fan-out, data caching, and RAID. host bus adapters (HBAs) and Ethernet NICs are types of I/O adapters.

A host computer software component (usually part of an operating system) whose function is to control the operation of peripheral controllers or adapters attached to the host computer.

I/O drivers manage communication and data transfer between applications and I/O devices, using host bus adapters as agents. In some cases, drivers participate in data transfer, although this is rare with disk and tape drivers, since most host bus adapters and controllers contain specialized hardware to perform data transfers.

Any path used to transfer data and control information between components of an I/O subsystem.

An I/O interconnect consists of wiring (either cable or backplane), connectors, and all associated electrical drivers, receivers, transducers, and other required electronic components. I/O interconnects are typically optimized for the transfer of data, and tend to support more restricted configurations than networks. See channel, device channel, network.

A property of an operation in which the same result is obtained no matter how many times the operation is performed.

In an environment with a single writer, writing a block of data to a disk is an idempotent operation, whereas writing a block of data to a tape is not, because writing a block of data twice to the same tape results in two adjacent copies of the block.

A form of addressing usually used with tapes in which the data's address is inferred from the form of the access request.

Tape commands that do not include an explicit block address but implicitly specify the next or previous block from the current tape position, from which the block address must be inferred by the device. Seeexplicit addressing.

In a system that implements in-band virtualization, virtualization services such as address mapping are performed by the same functional components used to read or write data. See out-of-band virtualization

An occurrence that actually or potentially jeopardizes the confidentiality, integrity, or availability of an information system or the information the system processes, stores, or transmits or that constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies. [NIST FIPS 200]

The INCITS T10 Technical Committee is the standards development committee accredited by INCITS to develop SCSI standards for communication between from host devices (initiators) to storage device controllers (targets).

A technique for reducing the time required to synchronize a split mirror with the set of storage devices from which it was split.

Incremental mirror resynchronization requires that a list of changes to the original set of data since moment of splitting be kept. When the split mirror is rejoined to its original set of volumes, only the data items identified in the list are copied from the original to the split mirror (rather than the entire contents of the devices).

Information assurance encompasses system reliability and strategic risk management, and includes providing for restoration of information systems using protection, detection, and reaction capabilities.

The policies, processes, practices, services and tools used to align the business value of information with the most appropriate and cost-effective infrastructure from the time information is created through its final disposition.

Information is aligned with business requirements through management policies and service levels associated with applications, metadata and data.

Virtualization implemented in the storage fabric, in separate devices designed for the purpose, or in network devices.

Examples are separate devices or additional functions in existing devices that aggregate multiple individual file system appliances or block storage subsystems into one such virtual service, functions providing transparent block or file system mirroring functions, or functions that provide new security or management services.

The cost of a system expressed in terms of the number and type of components it contains.

The concept of inherent cost allows technology-based comparisons of disk subsystem alternatives by expressing cost in terms of number of disks, ports, modules, fans, power supplies, cabinets, etc. Because it is inexpensively reproducible, software is generally assumed to have negligible inherent cost.

A worldwide federation of national standards bodies from more than 145 countries; a non-governmental organization whose work results in international agreements that are published as International Standards and other types of ISO documents.

A protocol specified by the IETF that performs mutual authentication between two parties and establishes an IKE Security Association (SA) that includes shared secret information that can be used to efficiently establish SAs for Encapsulating Security Payload (ESP) or Authentication Header (AH) and a set of cryptographic algorithms to be used by the SAs to protect the traffic that they carry.

A hardware or software signal that causes a computer to stop executing its instruction stream and switch to another stream.

Software interrupts are triggered by application or other programs. Hardware interrupts are caused by external events, to notify software so it can deal with the events. The ticking of a clock, completion or reception of a transmission on an I/O interconnect or network, application attempts to execute invalid instructions or reference data for which they do not have access rights, and failure of some aspect of the computer hardware itself are all common causes of hardware interrupts.

Originally used to mean a collection of disks without the coordinated control provided by control software; today the term JBOD most often refers to a cabinet of disks whether or not RAID functionality is present. See disk array.

A cryptographic protocol and procedure in which two communicating entities determine a shared key in a fashion such that a third party who reads all of their communication cannot effectively determine the value of the key.

A common approach to key exchange requires such a third party to compute a discrete logarithm over a large field in order to determine the key value, and relies for its security on the computational intractability of the discrete logarithm problem.

In the context of serial data communication networks, a solid-state element that emits light, usually in the near-infrared or infrared spectrum, modulated to carry binary information at very high data rates along an optical fiber.

The term laser was originally an acronym for "light amplification by stimulated emission of radiation."

An optical fiber connector complying with international standard IEC 61754-20:2002.

LC connectors are the most common connector in optical data communications networks, including Ethernet and Fibre Channel. A dual LC connector is used, carrying separate fibers for transmitted and received data.

Process of suspending the normal disposition or processing of records and Electronically Stored Information as a result of current or anticipated litigation, audit, government investigation or other such matters. [ISO/IEC 27050-1]

The issued communication that implements the legal hold can also be called a "hold," "preservation order," "suspension order," "freeze notice," "hold order," or "hold notice."

An IETFprotocoloriginally a subset of the X.500 protocolfor creating, accessing and removing objects and data from a directory.

LDAP provides the ability to search, compare, add, delete and modify directory objects, as well as modifying the names of these objects. It also supports bind, unbind and abandon (cancel) operations for a session. LDAP got its name from its goal of being a simpler form of DAP (Directory Access Protocol).

A communications infrastructuretypically Ethernetdesigned to use dedicated wiring over a limited distance (typically a diameter of less than five kilometers) to connect a large number of intercommunicating nodes.

A block of data stored on a disk or tape, and associated with an address for purposes of retrieval or overwriting.

The term logical block is typically used to refer to the host's view of data addressing on a physical device. Within a storage device, there is often a further conversion between the logical blocks presented to hosts and the physical media locations at which the corresponding data is stored. See physical block, virtual block.

A Fibre Channel primitive used to (1) initiate a procedure that results in unique addressing for all nodes, (2) indicate a loop failure, or (3) reset a specific node.

During a LIP, the nodes present on the arbitrated loop identify themselves and acquire addresses on the loop for communication. No data can be transferred on an arbitrated loop until a LIP is complete.

The average time from startup until a component failure causes a loss of timely user data access in a large population of storage elements.

Loss of availability does not necessarily imply loss of data; for some classes of failures, (e.g., failure of non-redundant intelligent storage controllers), data remains intact, and can again be accessed after the failed component is replaced.

The average time between a failure and completion of repair in a large population of identical systems, components, or devices.

Mean time to repair comprises all elements of repair time, from the occurrence of the failure to restoration of complete functionality of the failed component. This includes time to notice and respond to the failure, time to repair or replace the failed component, and time to make the replaced component fully operational. In mirrored and RAID arrays, for example, the mean time to repair a disk failure includes the time required to reconstruct user data and check data from the failed disk on the replacement disk.

Metered dispensation of resources appropriate to a given type of service (e.g., storage, processing, bandwidth, and active user accounts), such that usage can be monitored, controlled, reported and billed.

A network that connects nodes distributed over a metropolitan (city-wide) area as opposed to a local area (campus) or wide area (national or global).

From a storage perspective, MANs are of interest because there are MANs over which block storage protocols (e.g., ESCON, Fibre Channel) can be carried natively, whereas most WANs that extend beyond a single metropolitan area do not currently support such protocols.

The process of making the contents of a split mirror identical with the contents of the storage devices from which the mirror was split.

Mirror resynchronization may entail copying the entire contents of the storage devices, or when fast mirror resynchronization is used, only the data items changed in the original since the instant of splitting.

Distortion in the optical signal transmitted through a multimode fiber caused by different time delays for the various modes of propagation, resulting in a smearing of the signal edges that increases with the length of the fiber, thereby limiting the maximum length as a function of the data rate.

Monitors typically record CPU utilization, I/O request rates, data transfer rates, RAM utilization, and similar statistics. A monitor program, which may be an integral part of an operating system, a separate software product, or a part of a related component, such as a database management system, is a necessary prerequisite to manual I/O load balancing.

A security system that allows users and resources of different sensitivity levels to access a system concurrently, while ensuring that only information for which the user or resource has authorization is made available.

Naming is typically used either for human convenience (e.g., symbolic names attached to files or storage devices), or to establish a level of independence between two system components (e.g., identification of files by inode names or identification of computers by IP addresses).

The original, non-derived format and structure of data, together with its associated metadata.

Where data is unstructured, native file format means the original format of a file. While structured or unstructured data may be read by other programs, native data format means data whose state and integrity are unchanged since generation by its instantiating application.

An interconnect that enables communication among a collection of attached nodes, consisting of optical or electrical transmission media, infrastructure in the form of hubs and/or switches, and protocols that make message sequences meaningful.

A 4-bit field used to identify the controlling authority for guaranteeing uniqueness of World Wide Names (WWNs).

In a Fibre Channel environment, several Naming Authorities can be active at the same time, therefore Fibre Channel prepends the NAA field to World Wide Names to guarantee global uniqueness. An NAA =1, for example, indicates IEEE 48-bit Identifiers. The NAA also identifies one of several WWN formats, for example Format 1, Format 2 and Format 5.

A communications protocol that allows data storage devices, robotic library devices, and backup applications to intercommunicate for the purpose of performing backups.

NDMP is an open standard protocol for network-based backup of NAS devices. It allows a network backup application to control the retrieval of data from, and backup of, a server without third-party software. The control and data transfer components of backup and restore are separated. NDMP is intended to support tape drives, but can be extended to address other devices and media in the future. The SNIA has developed a v4 reference implementation, based on donation to it of the original code from NetApp and PDC.

NL-Ports are end points for Fibre Channel communication via Arbitrated Loop topologies that are attached to a Fabric, for example NL-Port to FL-Port to F-Port to N-Port using a single Fibre Channel Fabric switch. See F-Port, FL-Port, Nx-Port, L_Port.

The term node is used to refer to computers, storage devices, storage subsystems and network interconnection devices such as switches, routers and gateways. The component of a node that connects to the bus or network is a port.

Any form of tabular mapping in which there is not a fixed size correspondence between the two mapped address spaces.

Non-linear mapping is required in disk arrays that compress data, since the space required to store a given range of virtual blocks depends on the degree to which the contents of those blocks can be compressed, and therefore changes as block contents change. Seealgorithmic mapping, dynamic mapping, tabular mapping.

For communication, this may involve providing the sender of data with proof of delivery and the recipient with proof of the sender's identity, so neither can later deny having participated in the communication. Digital signatures are often used as a non-repudiation mechanism for stored information in combination with timestamps.

A state of a system in which the system is functioning within its prescribed operational bounds.

For example, a disk array subsystem is operating in normal mode when all disks are up, no extraordinary actions (e.g., reconstruction) are being performed, and environmental conditions are within operational range. Sometimes called optimal mode.

An NVMeoFC layer abstraction for an exclusive communication relationship between a particular NVMe host, connected via a particular initiator NVMe-Port, and a particular controller in an NVM subsystem connected via a particular target NVMe_Port.

NVRAM cache is particularly useful in RAID array subsystems, filers, database servers, and other intelligent devices that must keep track of the state of multi-step I/O operations even if power fails during the execution of the steps. It also allows arrays to reply to writes before they are committed to disk, as the NVRAM becomes the non-volatile store for the writes.

A "Node" port that connects via a point-to-point link to either a single N-Port or a single F-Port.

N-Ports handle creation, detection, and flow of message units to and from the connected systems. N-Ports are end ports in virtual point-to-point links through a fabric, for example the N-Port on an end node to F-Port on a switch to F-Port in that switch to the N-Port on the other end node using a single Fibre Channel fabric switch. An N-Port is assumed to always refer to an Nx-Port in a direct Fabric-attached PN_Port, and does not include NL_Ports